Drosophila numbers increase significantly in Idaho

The number of spotted wing drosophila caught in traps in southwestern Idaho has increased significantly the past few weeks. The pest attacks a broad range of fruit crops and producers in the region are monitoring the situation closely.

CALDWELL, Idaho — An exotic fruit fly that attacks a wide variety of fruit crops appears to have gained a foothold in southwestern Idaho.

The number of spotted wing drosophila caught in traps in the area has increased significantly over the past two weeks, raising the concern level of fruit producers around the region.

“They’re out there. They’re in the valley,” said Chad Henggeler, field manager for Henggeler Packing Co. in Fruitland, one of Idaho’s largest orchards. “We are very concerned about the situation and we’re … monitoring it all the time.”

Small numbers of spotted wing drosophila were detected in August of 2012 in Idaho but state officials were hopeful the state’s cold winters would prevent them from surviving over the winter.

However, the insect was detected in an orchard near Fruitland in June and University of Idaho researchers said the presence of the invasive pest that early in the 2013 season was an indication they may have over-wintered.

Unlike the common cherry fruit fly, which attacks ripe or already damaged fruit, the spotted wing drosophila will lay eggs in much firmer and thicker-skinned fruit while it is still on the plant.

“That can be a definite issue,” said Michael Williamson, manager of Williamson Orchards and Vineyards in Caldwell. “It’s a concern.”

It also has a broader range of hosts than other fruit flies, from berries and cherries to grapes and peaches.

The spotted wing drosophila prefers wet, cool weather and Idaho’s cold winters and hot, dry summers aren’t conducive to the pest, said Mike Cooper, bureau chief of the Idaho State Department of Agriculture’s plant industries division. But it does appear to have gained a foothold in this part of the state, he added.

“It’s probably here to stay,” Cooper said. “I don’t know how well it will do here, but it’s probably going to be a problem from time to time.”

ISDA and UI officials encourage fruit producers to harvest as early as possible to reduce exposure to the insect and to remove and destroy infested and overripe or damaged fruit.

The pest hasn’t damaged any good fruit at the Henggeler orchard but it can potentially cause economic harm and the company is watching it closely, Henggeler said.

“It’s become a new pest in our area and we want to be aware of it and keep an eye on the situation,” he said.

The insect was first detected in the mainland United States in 2008, in California, and was reported for the first time in Oregon and Washington the following year.

The fact that the insect attacks fruit that isn’t overly ripe or damaged is a major concern, said Bruce Pokarney, communications director for the Oregon Department of Agriculture.

“It’s been a major pest the last couple of years … and it seems to be more prevalent this year than last year,” said Pokarney, who added that Oregon State University researchers are working with growers to develop practices that can reduce the insect’s threat.